1. Technical Field
Example embodiments generally relate to an image forming apparatus using an electrophotographic, method, such as a copying machine, a printer, a facsimile machine, and a multifunction apparatus that combines the functions of the copying machine, the printer, and the facsimile machine. For example, example embodiments may be effectively employed in a tandem type full-color image forming apparatus. In addition, example embodiments generally relate to an upper frame opening and closing mechanism used in the image forming apparatus in which an upper frame including an image reading device, an automatic document feeder, an optical device, and so forth, is opened and closed relative to a main body including an image forming device.
2. Description of the Related Art
A related-art image forming apparatus, such as a copying machine, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor). An optical device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data. The electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor. A transfer device transfers the toner image formed on the photoconductor onto a sheet. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
In such an image forming apparatus, a toner is consumed over time and is usually resupplied by replacing a toner cartridge. For example, the image forming apparatus includes a main body including an image forming device, and an upper frame including an image reading device, an automatic document feeder, an optical device, and so forth. The upper frame is pivotally attached to the main body, so that the upper frame can be opened and closed relative to the main body on a hinge. The image forming device in the main body is exposed when the upper frame is opened upward, so that a waste toner cartridge can be easily replaced with a new one. Moreover, jammed sheets can be easily removed by opening the upper frame.
However, in a tandem type full-color image forming apparatus in which toner cartridges of four colors are provided in the main body, the upper frame must open wide in order to take all four toner cartridges out of the main body. Also in an image forming apparatus in which a user can perform all operations from a front side thereof, the upper frame must open wide in order to take toner cartridges out of the main body from the front side of the image forming apparatus.
To meet the above-described requirements, a related-art image forming apparatus includes an arm member, a base end of which is pivotally mounted on the upper frame, and a rail member for guiding a leading edge of the arm member along with opening and closing of the upper frame, provided on the main body. The related-art image forming apparatus further includes a biasing member for biasing the upper frame in an opening direction so that the upper frame can be widely and stably opened.
However, in the related-art image forming apparatus described above, when the user releases the upper frame during the opening motion before an opening angle of the upper frame exceeds an inversion angle θ, which is an opening angle of the upper frame when a center of gravity G of the upper frame reaches a vertical surface V passing a fulcrum F as illustrated in FIG. 38A, the upper frame receives a moment in a closing direction due to gravity. Consequently, the upper frame 30 returns to a closed position, and collides with the main body with great force as illustrated in FIG. 38B, possibly causing injury and damage. On the other hand, when the user releases the upper frame during the opening motion when the opening angle of the upper frame exceeds the inversion angle θ, the upper frame receives a moment in an opening direction due to gravity. As a result, the upper frame is opened backward due to gravity as illustrated in FIG. 38C, and may collide with a person or an object behind the image forming apparatus. The weight of the upper frame increases if the upper frame includes the image reading device, for example, the automatic document feeder, the optical device, and so forth, thus exacerbating the aforementioned problem. Accordingly, the upper frame may be pivotally opened backward with great force, possibly causing injury, large noise, and damage to components.
To solve such problems, another relate-art image forming apparatus includes one or both of a pivot spring provided to the hinge, and an arm spring provided to the base end of the arm member. The pivot spring biases the upper frame in the opening direction at first when the upper frame is opened, and reversely biases the upper frame in the closing direction during the opening motion. The arm spring pivotally biases the arm member, and initially applies a moment to the arm member in the opening direction when the upper frame is opened, and reversely applies a moment to the arm member in the closing direction during the opening motion. With such a configuration, the upper frame can be prevented from being fully opened and closed with great force, preventing injury and damage. In addition, an impact caused by the opening and closing of the upper frame can be cushioned.
However, in the above-described configuration, prevention of damage and impact caused by the opening and closing of the upper frame is performed by a single spring having functions of both of the pivot spring and the arm spring, such as a torsion spring. Therefore, it is difficult to adjust the pivot spring and the arm spring to reliably prevent injury and damage caused by the opening and closing of the upper frame, as well as to securely reduce the impact.